This invention relates to threaded fasteners and more particularly to a fastener assembly that automatically maintains self-tightening force after its installation.
Many types of structural arrangements, utilize threaded type fasteners, such as common hex nuts in combination with bolts, tie-rods and the like to maintain structural integrity. Although the nuts may be originally installed and tightened with an adequate amount of torque, there are often extraneous forces or conditions affecting the installation which can either cause the nut to become loose or require additional take-up turning in order to maintain the intended bolt or rod tension and thus the integrity of the installation.
To further complicate the problem, the forces or conditions causing the loosening or tension reducing condition may occur over a period of time and be inherently difficult to detect without an elaborate monitoring or checking system. Moreover, in many structural installations the nuts which may tend to loosen or require tightening over a period of time are located in totally inaccessible or difficult to reach places within a structure.
One example of the need for such a self tightening nut type fastener occurred with respect to a structural tie-rod strengthening system for wooden buildings such as described in United States patent application Ser. No. 000,707, filed Jan. 6, 1987, and assigned to the owner of the present invention. In such tie-rod installations, the threaded nut fasteners were initially tightened with a high level of torque to place the tie rods in tension between wooden structural members. Such installations were often made in new buildings where the construction lumber was relatively green. Over a period of time the green lumber underwent a normal shrinkage which caused the tie-rods to lose tension and their fastener nuts to become loose. Such conditions greatly reduced the strengthening effectiveness of the tie-rod system on the building particularly during high stress conditions such as produced by heavy wind or earthquake loads. To alleviate this potential danger on the aforesaid and other structural arrangements, it was necessary to provide a nut type fastener for a threaded body that would automatically tighten itself if, for some reason, the resisting force decreased or a looseness occurred with the threaded connection.
A general object of the present invention is to provide a self-tightening fastener device that solves the aforesaid problem.
Another object of the invention is to provide a self-tightening fastener device that is relatively easy to install even in space limited situations and without the need for highly skilled labor or complicated tools.
Still another object of the present invention is to provide a self-tightening fastener that utilizes stored potential energy to maintain a take-up torque for an extended period of time and will automatically respond to any tendency of the fastener to loosen after initial installation.
Another object of the invention is to provide a self tightening fastener device that is particularly well adapted for ease and economy of manufacture.